Stone fountains such as the granite piece I used have a hole at the bottom, where you insert the pump's tubing. But the stone fountain, for that reason, needs to be elevated off the pond's bottom (so that you have access to this hole). The solution is to use a metal grate that will support the stone fountain. The tubing needs to be able to move freely underneath both the stone fountain and the metal grate.
A number of different kinds of metal grates would work here. Some might run across the top of the pond liner; unless very sturdy, this type might need to be supported by cinder blocks placed in the pond. Depending on the material of your grate and on your personal preferences, you may wish to paint the grate to prevent rusting (thanks to reader, Carole for this suggestion).
My grate (shown in the picture here, along with the pond liner) is a bit different because, as mentioned earlier, I improvised and used a cast iron grate meant for holding firewood. As you can see from the picture, this metal grate will fit nicely within my pond liner. I had it on hand and figured, "Hey, after spending $250 on a hunk of rock, why not save a little money?"
In Step 4 you'll see the metal grate in action....